Arthritic damage to portions of the knee joint can severely limit an individual's ability to walk or enjoy recreational activities. The extent of arthritic damage may be far reaching, affecting all compartments of the knee joint, or the damage may be limited to a single compartment of the knee (“unicompartmental osteoarthritis”), requiring only resurfacing or replacement of a single surface rather than total knee replacement surgery. In understanding unicompartmental joint reconstruction, practitioners typically refer to three separate areas of joint articulation as if they were separate compartments: the inner part of the joint between femur and tibia (the “medial compartment”), the outer part of the joint between femur and tibia (the “lateral compartment”) and the joint between the patella and the femur (the “patello-femoral compartment”). If osteoarthritis affects a patient only in the lateral or medial compartment of the knee, unicondylar knee arthroplasty often is a preferred method of treatment, as the surgery is far less invasive, and allows for more rapid recovery while maintaining the integrity of unaffected areas of the knee, often allowing the anterior and posterior cruciate ligaments to remain intact.
As such, unicondylar knee arthroplasty has gained popularity in the recent years for treating medial compartment osteoarthritis of the knee joint, and has proven to be a successful surgery for people with this degenerative arthritis of the knee. The inside (medial) component (medial tibial plateau and the medial femoral condyle) is most commonly involved and replaced using unicompartmental arthroplasty. However, occasionally, the outside (lateral) compartment (the lateral tibial plateau and the lateral femoral condyle) is involved and must be replaced.
While a unicondylar arthroplasty is far less invasive on the patient, it should be appreciated that when only a single condyle of the tibia is resurfaced and replaced with an implant, there is less surface area to attach an implant and receive anchors to secure the implant that will receive stresses in nearly all directions almost immediately after the surgery is performed. Traditionally, bone cement was used to secure such an implant into place, thereby securing the implant and filling any voids between the contoured condyle and the bottom surface of the implant. However, bone cement can weaken and crack over time, causing failure of the implant, and/or creating debris within the knee compartment. The flexing motion of the knee is known to cause an implant on the tibial plateau to lift off anteriorly, which also may cause failure of the implant and/or produce debris within the knee compartment. Further, any excess cement that is not cleared from the compartment during surgery can cause inflammation or result in debris within the compartment.
Efforts to improve long term success of tibial implants and reduce the inflammation or failure that can be caused by the use of bone cement include the use of highly porous metal or Trabecular Metal implants to encourage better bone growth into the implant for long term retention of the implant, but securing such an implant through the ingrowth of the patient's cancellous bone requires a significant amount of time, and proper integration requires that the implant be securely held in place while the integration occurs. Considering the significant forces associated with weight bearing and activity as distributed over the small surface area of the tibia, there is concern that porous implants may not be retained in place during the ingrowth of cancellous bone required to maintain the implant during the healing phase. For example, the flexing motion of the knee is known to cause a tibial baseplate to lift off anteriorly, hindering bone ingrowth in a porous metal implant. As such, an implant having an ability to be secured to the anterior medial condyle of a tibia without the use of bone cement would be advantageous.